Yep, The Furies is the one I'm waiting on at the moment.
I found it fascinating. I didn't expect the level of brutality, maybe because most post-apocalyptic novels I've read assume that many more animals and much more technology survived. (Well, and many more humans, too). I liked Motherlines better, though, because I loved the intricacy of the Riding Woman culture.
Some of my students might have heard of the concepts. It's just not something I can take for granted.
Yeah, it's pretty horrific. I suspect part of what Charnas was doing with the first book was to build the most vicious, horrible patriarchal society she could and still see if she could make it work (and if she could avoid focusing simply on how horrible and evil it was). For the record, I think raising the female children in pits 24/7 for several years would create non-functional human beings, useless for anything -- assuming they even survived such treatment. But for the most part, it's scarily plausible.
Don't know how much and how many spoilers you want, but in The Furies, the post-collapse patriarchal Holdfast culture is not quite as vicious. It no longer has the means or the organization to be.